Method of and apparatus for controlling the resistance of an x-ray tube.



E. W. KELLY. METHOD 0F AND APPARATUS FOR CONTROLLING THE RESISTANCE 0F AN X-RAY TUBE.

APPLICATION FILED DEC. 26. I9I3. 1,285,215. Patented N0v.19,1918.

3 SHEETS-SHEET l.

E. W. KELLY. ONTROLLTNG THE RESISTANCE 0F AN xRAY TUBE.

' APPLICATION FILED DELZG. 1913. 1,285,215. v Patented Nov. 19, 1918..

3 SHEETS-SHEEY 2.

v.METHOD 0F AND APPARATUS FOR C /NVEN TOR Vw/'T/wssEs w BY ' ATTORNEY E. W.. KELLY. METHOD 0E AND APPARATUS EDIT CONTRDLLING THE RESISTANCE oF AN x-ITAY TUBE.

APPLICATION FILED DEc.2s. T913.

1 ,285,21 5.. Patented Nov. 19, 1918.

` a SHEETS-SHEET 3.

/N VEN TOR` Y w/ TNESSES ym BY 226% UNITED STATES PATENT OFFICE.

IEDIN` WALKER KELLY, OFPHILADELPHIA, PENNSYLVANIA,

ASSIGNMENTS, TO VICTOR ELECTRIC PORATION 0F NEW YORK.

ASSIG-NOB, BY MESN E CORPORATION, OF CHICAGO, ILLINOIS, A COR- METHOD OF AND APPARATUS FOR CONTROLLING THE RESISTANCE 0F AN X-BAY TUBE.

Specification of Letters Patent.

Patented Nov. 19, 1918.

Application led December 26, 1913. Serial No. 308,668.

My invention relates to a method of andd apparatus for controlling the behavior of vacuum tubes, and more particularly X-ray tubes.

It has long been known that the vacuum or highly rarefied air remaining in a glass bulb which has been highly exhausted is a very perfect non-conductor of electricity and that even a potential as high as that ever impressed on an X-ray tube will not send a discharge between electrodes Wit-hin the bulb if the exhaustion has been-pushed far enough. And it has further been long known that if in such a highly exhausted bulb electrodes are provided, for example one of them a metal plate and the other a carbon filament, like an incandescent lamp filament, no discharge will passl between the filament and plate when the lament is cold, but, when the carbon filament .is rendered incandescent as by passing a current through it, it is found that even slight potentials, such as developed by a single Vcell of battery, will pass current through the vacuum space between the hot filament and the plate provided that the hot filament is made the negative electrode with respect to the source of applied potential.

This phenomenon has been explained by stating that the incandescent body throws oif into the evacuated space what are termed corpuscles which are themselves electronegatively charged masses or particles, the smallest particles into which matter is divisible. And it is explained that the introduction of these corpuscles in effect ionizes the vacuous space so that electricity may pass therethrough. In a sense therefore Y conducting vacuous space conducting.

According to my invention this principle or phenomenon is availed of to control the behavlor of a vacuum tube or bulb, and more. particularly an X-ray tube or bulb.

For an illustrationof a mode of practice of my method and of apparatus suitable therefor, particularly in connection with X- ray tubes, reference is to be had to the accompanying drawings, in which:

Flgure l is a fragmentary side elevation, parts in longitudinal section, of an X-ray tube having applied' thereto one form of vmeans for carrying out my invention.

Fig. 1El is a front. elevational view of the cathode of Fig. l.

Fig. 2 is a longitudinal section through the cathode stem of an X-ray tube and parts therein, some being shown in elevation, pro vided with a different form of means for carrying out my invention.

Fig. 2a is a front elevational view ofthe cathode and the lament of Fig. 2.

Fig. 3 is a longitudinal section similar to that in Fig. 2 showing further means for carrymg out my invention.

Fig. 3a is a cross sectional view, parts in sect-ion, taken on the line A-A of Fig. 3.

Fig. et shows a cathode isolated from the tube together with a modified form of incandescing member.

Fig. 4f* is a perspective v iew of the parts shown in Fig. 4.

Fig. 5 is a longitudinal sectional view through a modifie'd form of cathode the filament shown in elevation.

Fig. 6 is a sectional vies7 through a further modiiication of a cathode and lament.

Fig. 6a is a front elevational view of the cathode of Fig. 6.

Fig. 7 is a fragmentary longitudinal sectional view of a cathode system of an X-ra tube having a modified form of cathode therein. Y

Fig. 7a is a perspective view of the cathode shown in Fig. 7.

Fig. 7 b is a front elevational view of the same.

Figs. 8 to l1 inclusive are diagrammatic views of different modifications of arrangements of electrical circuits that may be employed in practising my invention.

Referring to Fig. 1, X is a glass bulb of an iii-rar tube. haring the usual anode stem u. tromD which is supported the anode or target A, the bulb haring aise the usual cathode stein e Within 1which is supported the cathode C disposed upon the conducting rod I supported in the inner glass stem ol and elcetricaiiy connected to the wire or other suitable conductor hl sealed in the glass at the end ot the stem e in the Weil known manner. the nire El connecting With the negative pole oit' the source ot high potential current tor operating the Lray Jpube, as in 'the 1eveil hnou'n prior practice. in a caritv e in the cathode C is disposed the tilanieut f5 such as un incandescent lamp iilament` preferably ot tungsten, tantalum,

latinuui or any other suitable material adapted to be raised to high tenipe'ature or incandcscence by a current passed therethrough the source ot said current haring its one terminal connected outside of the X-rav tube "with 'the conductor lli and its other terminal connected outside ot the L ray tubeV with the conductor g which is sealed through the glass nail ot the tube and connects with one terminal ot the filament j", through insulating bushing hl, the other terminal ot the ianient ,t connecting with conductor extending through bushing 71.. rhe conductor j may connect to the cathode @C at any suitable point either outside or inside ot" the tube. in the eX- aiupie illustrated the conductor j connects to the conductor l within the glass seal. lfthe conductors g und j may be supported by the glass buttons la, upon the inner glass stem d'. Set in the cathode t is a dish or plate m-g of tungsten, tantalum or any suitable materiniE the ii'ament f being disposed close thereto .at its rear. The surface contour ot dish m conforms as nearly as is possibie or roni'enient to that ot' the cathedc.

rihe Lray tube hating been highly ex hausted and sealed eti at. u. it the space Within the tube is very highly rareed, as for example to a degree such that current u'iil sooner leap through the air across an air gap between terminals outside ot the tube electrically connected to the anode and cathode and separated, tor example, teu inches. no current will pass Within the tube between the anode and cathode; but when the lilainent yi is raised to incandescence by current passed therethrough heat therefrom is transferred to the metallic disltvm which in turn is raised to rery high temperature, as for example, incandesccnce, and then the corpuscles or negatireiy charged particles are thrown ott into the vucuous space and the tube n'iil conduct eurrent delivered by the high potentiel source, By adjusting the amount oit current passed through the tilement the. tempereture ot the dish m may he regulated or determined and the conducmessie tiyity' or resistance ot the X-ray tube X controlled or determined. Bind while the tube, in the example assumed, would not conduct energy upon the application of a; potential high enough to produce av spark across an air gap ot ten inches outside of the tube, it will nou' conduct current upon the application ot such a potential aud indeed of much lower potentials, such, tor eX- ample, as are capable of causing sparking across only three or four inches ot air gap outside ot the tube.

ind While it is above assumed that the lli-ray tube has been pumped or exhausted to a very great degree, it is to be understood that my invention is applicable also to the case Where the exhaustion isnot carried so tar and Where there is substantial remanent gases, either remaining after the pumping y or existing atter the X-ray tube has been operated some time.

in either case however the liberation of the corpuscles atiords a mode of controlling the conductivity or resistance of the `hrt-ray tube.

For example, a physician operating an Iii-ray tube, may close the switch affording communication between the source of high potential current and the terminals of the X-ray tube and thereafter close or regulate the resistance ot the filament circuit to conv trol the temperature of the disk m. By adjusting the temperature ot the disk m by adjusting the current through the filament 7' he may procure from his -ray tube practically any character ot X- nys, for example, Xmays of different, penetrations and qualities.

And by my invention this manipulation or control ot' the -ray tube is greatly simplified in that the X-ray tube electrodes, namely the X-ray tube cathode and anode are themselves employed for the ionization ot the vacuous space to the condition for conductivity or desired degree ot conductivity without ,recourse to an additional or seperate circuit Jtor ionization purposes.

l'n the structure above described the ila ment f does not itselt' provide the corpuscles, but. the disk m provides them, the filament j operating only indirectly for this purpose.

The incandescent tilament may however operate to itself directly supply the corpuscles in which case the arrangement may be such as shown in Fig. 2. Here the filament 7 is supported by the glass member 0 carried by the inner glass stem d, the ilament being disposed in a notch p in the cathode C. Here the filament connecting Wires j and g are connected respectively `with the negative conductor N and a source ot filament exciting current as in F ig. 1. i

Here when the filament f is raised to suitn ie temperature by current passed therecommunication with the cathode through it will liberate corpuscles or negatively charged particles with resultant adjustment or control of the conductivity or resistance of the X-ray tube.

In Fig. 3 the arrangement is similar to that in Fig. 2 except that the cathode C is not notched and the Vfilament. f is disposed back of the cathode C, the electrical connections being the same as in Fig. 2. Supported by the cathode C on pins or rods g is the metallic electro-static shield 1 in electrical C through the rods g. The shield r is disposed between the filament f and the glass cathode stem c for the purpose of neutralizing any electrostatic attractive effect upon the filament f which would otherwise cause it to deflect over toward and possibly become welded or attached to the inside wall of the glass stem c.

It is to be understood that the electrostatic shield 7 may be applied to structures other than that shown in Fig. 3 by simple application of the principle of its action above described.

In Figs. 4 and 4 the filament takes the form of an incomplete ring f surrounding the cathode C back of its active Surface and standing free therefrom, being supported by wire or other supports s anchored at s to the inner glass stem d. To the ends of the ring f are connected the filament clrcuit conductors g and j for conveying current to the filament as in the cases above described.

In Fig. 5 the cathode C is provided with a hole or Yaperture t communicating with the cavity e within which is disposed the filament f carried by the glass support o carried by the metallic plug u. One end of the filament connects by Wire j with the cathode C while the other passes through insulating bushing u and connects with wire g which extends to the exterior of the tube as in the previous cases described.

In this case again the filament is raised t0 suitable high temperature whereupon the corpuscles or negatively charged particles emanating therefrom escape into the space of the X-ray tube through the aperture t with the results hereinbefore described.

In Figs. 6 and 6a the cathode C is pro- 'vided in its front or active face with a depression or recess 'v within which is disposed the filament f whose one end y" connects directly with the cathode C and whose other terminal connects through conductor g, passing through insulating bushing L" and extending to the exterior of the tube as in the other cases described.

` In the arrangement shown in Figs. 7, 7a and 7b the cathode C' is made of thin sheet metal or other suitable materia-l provided with the conducting tongues or extensions w and ic of relatively thicker or heavier section than the cathode C. The tongue w is electrically and mechanically connected to t-he cylindrical or similar metallic' cu whose cylindrical edge is sealed into a liollow circular glass portion y on the hollow inner glass stem d', the wall of this portion 7o opposite the stem d being rounded outwardly, and the conductor N electrically connects with the tongue w through the member and extends to the outside of the X-ray tube through the tube d where it is connected, as previously stated, with the negative pole of the source of high potential current for operating the X-ray tube. The other tongue w is similarly connected to and supported by the metallic cup member sealed into the hollow glass button y. The stem d i's hollow as shown, the inner end wall being indicated at y and access into the interior of the stem d may be had from outside of the X-ray tube, the entry to the hollow tube d being at d. The tongue fw is electrically connected through the member so with the conductor g which extends to the exterior through the tube d',

In this case a relatively heavy current is passed through the cathode C itself from a source of energy whose terminals are connected to the conductors N and g, This current raises the temperature of the cathode C itself to the desired point where it will liberate corpuscles or negatively charged particles at the rate desired, it being remembered that it is connected to the negative pole of the high potential source through conductor N. 10

Because of the circular shape of the cathode CAits thickness may vary from its center to its periphery along the horizontal dotted line in Fig. 7b in such manner that the resistances of the myriad conducting paths between the tongues lw andy w may""""`f be substantially equal. In such case the thickness of the cathode C at its center is less than at its periphery, and roughly speaking, it is about one and one half times as thick at its periphery as at its center.

lVith the structure illustrated in Fig. 7 the cathode itself direcly supplies the conductivity controlling corpuscles.

In Fig. 8 X is an X-ray tube provided 115 with any of the forms of means for liberating corpuscles, such as those hereinbefore described or their equivalents. The X-ray tube is excited from a source of high potential current, such, for example, as a high 120 potential rectifying system disclosed in prior Letters Patent of the United States No. 954056, comprising the high potential rectifying switch R intervening between the X-ray tube 'X and the high potential step- 125 up transformer T whoseprimary, adjustable as to its number of turns by the movable contact l, receives current through the adjustable resistance 2 through the reversing switch 3 from the alternating current 180 be produced by generator t driven by the electric motor 5 receiving current from the mains or supply conductors 6 and 7. i The anode A of the X-ray tube X conneet-s with the positive terminal of the source ot high potential current through the conductor 8 while the cathode, as hereinbetore explained, connects through conductor N With the negative pole of the source of high potential current. Connected in parallel relation With the ,X-ray tube anode and cathode are the spark gap terminals 9 and l0 for measuring by means of a gap in air out side of the tube the relative resistance of the X-ray tube. The conductor g leading to one terminal of the iilament or heating element, as hereinbetore described, connects through adjustable resistance 11 and switch 12 with the terminals of the alternating current generator 4 whereby, When the switch 12 is closed, current will flow from one terminal of the generator 4 through the conductor g and through the heating element, or iilament such as hereinbefore described, to conductor N and thence through conductor 13 and adjustable resistance 11 to the other terminal of the generator et.

The physician or operator closes the line switch 1% and brings the motor 5, generator at, rectiying switch R up to speed. He thenl closes the switch 3 and adjusts the resistance 2., or Contact 1, or sired high potential delivered by the rectirying switch RG. Current Will not pass through the Xmay tube X at the desired potentiai applied, for reasons hereinbefore given, that is, because of the great degree of vacuum in the tube X; or the condition Within the tube may be such that current will pass under the iniluence of this applied potential but in insutiicient quantity. in either case he may then close the switch 12 and Vadjust the resistance 11 until sufficient corpuscles or negatively charged particles are delivered into the vacuous space to produce the desired conductivity or resistance of the X-ray tube X. Or he may first close the switch 1Q; and adjust the resistance 11 to a previously determined point for which it is known a certain character of rays Will the tube, and he may then close the switch 3 whereupon current will pass through the Y-ray tube and produce X-rays in the Well known manner, and when the current through the heating element or iilament is reduced or broken the current from the high potential source through the X-ray tube will diminish or cease.

l't will he noted that in this case, Where the lament or heating element derives current through a circuit which is conductively connected to the alternating current generator a, the negative conductor hl is connected to earth E.

ln Fig. 9 the errafigeanentr is similar to both, to produce the derestare that in Fig. 8 except that here the current delivered to the iilament or heating element is derived from the direct current supply, or the mains of Whatever type of supply, through the adjustable resistance 11 and the switch 12. j Here again the negative conductor N is connected to earth E.

ln Fig. 10 the connection to earth E may be omitted, since the circuit through the filament or heating element through conductor g is insulated trom both the supply conductors and the alternating current generator 4 in that the current through the conductors g' and 13 leading to the heating element or filament is derived from the secondary 15 of a small preferably step down transformer T Whose primary Winding 16 connects With the terminals of the alternating current generator 4 through the adjustable resistance 17 and the switch 1Q. In this case the temperature of the tilament or heating element may be determined or adjusted by adjusting the resistance 11 or resistance 17, or both.

In Fig. 11 is a fragmentary illustration of an arrangement whereby the lament 7, or any other similarly operating heating element or corpuscle delivering element may be traversed by a source of current separate and distinct from that operating the X-ray tube. Here a battery or other source of current 18 has its one terminal, preferably its positive terminal, connected with the conductor g through the switch 12 While its negative terminal connects through the adj ustafbjle resistance 11 with the conductor VN. Here again the adjustment of the resistance 11, after closure of switch 12, will determine the temperature of the lament f and therefore the conductivity or resistance of the X-ray tube Whose cathode is C.

'What l claim is:

1. The method of increasing the conductivity of an X-ray tube having an attenuated atmosphere ot free gas and main electrodes which are solid, which consists in creating a potential differencebetween the terminals of the main path of the X-ray tube, rendering a body Within said tube electro-negative by subjecting it to substantially the potential of the negative terminal of said main path, and raising said body to a temperature causing emission of corpuscles for increasing the conductivity of said main path.

2. rthe method of controlling the conductivity or a vacuum tube, which consists in impressing a high potential upon the anode and cathode of a vacuum tube, rendering a body in said tube disposedfnear the cathode thereorn electro-negative by subjecting the same to said same high potential, and rais-4 ing the temperature or" said body by passing a current therethrough.

3. lfhe method or' controlling the conductivity or an -ray tube, which consists in impressing a high potential upon the anode and cathode of an X-ray tube, rendering a body in said tube disposed near the cathode thereof electro-negative by subjecting the same to said same high potential, and raising the temperatureof said body by passing a current therethrough.

4. The combination with an X-ray tube and its separated anode and cathode for producing X-rays, of means for raising the temperature of said cathode to incandescence, and means for passing current through said means.

5. The combination with an X-ray tube and its separated anode and cathode for producing X-rays, of means for passing near said cathode to raise its temperature a current independent of the tube exciting current.

6. The combination with a vacuum tube and its separated anode and cathode, of a source of high potential current having its negative terminal connected to said cathode, of a conductor Within said tube connected to said negative pole of said high potential source, and a second source of current for passing current through said conductor to raise its temperature.

7. The combination With an X-ray tube and its separated anode and cathode, of a source of' high potential current having its negative terminalconnected to said cathode, of a conductor Within said tube connected to said negative pole of said high potential source, and a second source of current for ,passing current through said conductor to raise its temperature.

8. The combination with a vacuum tube and its separated anode and cathode, of a source of high potential direct current having its negative pole connected to said cathode, of a conductor lWithin said tube near said cathode and connected to said negative pole of said source of current, and a second source of current for raising the'temperature of said conductor.

9. The combination with an X-ray tube and itsseparated anode and cathode, of a source of high potential current having its negative pole connected to said cathode, of a conductor Within said tube near said cathode and connected to said negative pole of said source of current, and a second source of current for raisingthe temperature of said conductor.

10. The combination with aA vacuum tube and its separated anode and cathode, of a source of high potential direct current having its negative terminal connected to said cathode, of a conductor Within said tube connected to said negative pole of said high potential source, a second source of current for passing current through said conductor to raise its temperature, and means for controlling the strength of the current through said conductor.

11. The combination with an X-ray tube and its separated anode and cathode, of a source of high potential current having its negative terminal connected to said cathode, of a conductor within said tube connected to said negative pole of said high potential source, a second source of current for passing current through said conductor to raise its temperature and means for controlling the strength of the current through said conductor.

12. The combination With a vacuum tube and its separated anode and cathode, of a source of high potential current having its negative pole connected to said cathode, of a conductor Within said tube near said cathode and connected to said negative pole of said source of current, a second source of current for raising the temperature of said conductor, and means for controlling the strength of the current through said conductor.

13. The combination with an X-ray tube and its separated anode and cathode, of a source of high potential current having its negative pole connected to said cathode, a conductor within said tu-be near said cathode and connected to said negative pole of said source of current, a second source of current for raising the temperature of said conductor, and means for controlling the strength of the current through said conductor.

14. The combination With a vacuum tube and its separated anode and cathode, of a source of high potential current having its negative pole .connected to said cathode, a filament Within said tube in electrica-l communication with said negative pole of said source of current, and a second source of current for raising the temperature of said filament.

15. The combination with an X-ray tube and its separated anode and cathode, of a source of high potential current having its negative pole connected to said cathode, a filament Within said tube in electrical communication with said negative pole of said source of current, and a second source of current for raising the temperature of said filament.

16. The combination with a vacuum tube and its separated anode and cathode, of a source of high potential current having its negative pole connected to said cathode, a lilament disposed Within said tube near said cathode and electrically connected with said negative pole of said source, the shortest distance between said anode and said cathode being less than that between said anode and said filament, and a second source of current for raising the temperature of said filament.

17. The combination with an X-ray tube and its separated anode and cathode, of a source of high potential current having its negative ole connected to said cathode, a filament disposed within said tube near said i cathode and electrically connected with said negative pole ot' said source, and a second Source of current for raising the temperature of said filament.

'18. The combination with the Vacuum tube and its separated anode and cathode,

i of a source of high potential current having its negative pole connected to said cathode, a filament within said tube in electrical coininunication with said negative pole of said source of current, a second source of current Afor raising the temperature of said filament,

and means for adjusting the current through said filament.

19. rlhe combination'with an X-ray tube and its separated anode and cathode, ot a source of high potential current having its negative pole connected to said cathode, a filament Within said tube in electrical communication with said negative pole oit said source of current, a second source otcurrent for raising the temperature of said ulament, and means for adjusting the current through said filament. Y

20. rlhe combination with an anode and a solid cathode. of a vacuum tube, ot a source of high potential" connected thereto, a conductor Within Said tube maintained electronegative, at high did'erence of potential with respect to said anode and at approximately the saine potential as said cathode, and means for raising the temperature of said conductor.

2l. The combination With the anode and cathode of an X-ray tube, ot a source ot high potential connected thereto, a conductor within said tube maintained electro negative, at high difference of potential with respect to said anode and at approximately the saine potential as said cathode, and ineans for raising the temperature of said conductor.

22. T he combination with an anode and a solid cathode of a vacuum tube, of a source of high potential connected thereto, a. conductor Within said tube maintained electronegative, at approximately the same potential as said cathoden and at high difference of potential with respect to said anode, and means for passing current through said conductor to raise its temperature.

23. The combination with the anode and cathode of an X-ray tube, of asource ot1l high potential connected thereto, a conductor within said tube maintained electro-negative, at approximately 'the salue potential as said cathode, and at high difference of potential with respect to said anode, and means for passing current through said conductor to raise its temperature.

2t. The combination with an anode and a solid cathode of a. vacuum tube, of a source of current, ineens deriving energy from said source for impressing high potential upon said anode and cathode, a conductor Within incanta said tube connected with the negative pole of said high potential ineens, and ineens deriving energy from said source otcurrent for passing current through said conductor to raise its temperature.

25. The combination'with theanode and cathode ot an X-ray tube, ot a source ot alternating current, means deriving high potential energy troni said source for iinpressing said high potential upon said anode and cathode, a conductor Within said tube connected with the negative pole ot said high potential ineens, and a transtoriner deriving current from said source ot alterhating current for passing current through said conductor to raise its temperature.

26. The combination with an -ray tube having an attenuated atmosphere ot tree gas, of an anode and cathode spaced trom each other within said gas, a source ot high potential current connected to said anode and cathode, a body within said tube subjected to substantially the same negative potential as said cathode, and means tor independently heating said body to a temperature to einit corpuscles to increase the conductivityot the tube. Y

27. ln an )l-ray tube the combination of an anode; a cathode; a circuit for said anode and cathode; a ilarnent located in said tube adapted `when hot to send radiations into the space between said anode andcathode; a second circuit tor heating said iilainent; and a connection between said niet and sec-` ond named circuits, substant'ally as described.

28. ln an X-ray tube the combination of an anode; a cathode; a circuit tor said anode` and cathode; a lilament located in said tube adapted when hot to send radiations into the space between said anode and cathode; a second circuit for heating said blament; a switch and an adjustable resistwce in said second circuit; and a connection between said first and second named circuit-s, substantially as described.

29. The method of controlling the conductivity ot a vacuum tube, which consists in impressing greatly diderent potentials upon the main electrodes respectiely, simultaneously impressing a lon' potentiai upon a body within said tube, and raising the temperature ot' said body to such a degree that one of the niain electrodes is heated thereby'to cause negatively charged corpuscles to be emitted, said body being never at a potential higher than that of the main electrode which is charged to the higher potential.

30. The combination with an -raj: tube and its separated anode and cathode tot' producing K-rays, of means spaced troni said cathode for raising the temperature of said cathode to incandcscence, a d means for passing current through saidnieans.

Bl. he combination with the anode and said recess cathode of a vacuum tube, of a body disposed behind said cathode and shielded thereby from bombardment impinging upon the front of said cathode, and means'for raising said body to a temperature for emitting corpuscles. Y

32. The combination with the anti-cathode and cathode of an X-ray tube, of a body subjected to substantiallynthe same potential as said cathode and disposed behind the same and shielded thereby from bombardment im pinging upon the front of said cathode, and means for independently heating said body to a temperature to emit corpuscles.

33. An X-ray tube comprising an anticathode and a cathode structure co erating therewith 'having a corpuscle-emitting part of small heat capacity, a conductor disposed near said part to heat the same, and means for maintaining said conductor at a temperature which will cause said part of small heat capacity to glow.

34. In vacuum tube apparatus, the combination with a cathode having a concave active surface and a portion disposed near the center of said surface havinga small heat capacity, of heating means disposed near said portion to maintain said portion at a high temperature during operation.

35. In vacuum tube apparatus, the combination with a cathode comprising an element having a recess therein, one wall of being of thin metal, of a heating coil in said recess, and means for supplying current to said coil.

36. In vacuum tube apparatus, the combination with an electrode comprising an element having a recess therein, of a heating coil in said recess, terminals for said heating coil, one of said terminals being in electrical connection with said element, and a source of heating current connected to said terminal.

37. An X-ray tube comprising" an anticathode, a. concave cathode for focusingcathode rays upon an anti-cathode, a body disposed near said cathode and subjected to substantially the same potential, and means for independently heating said body to a temperature to emit corpuscles.

38. An X-ray tube comprising an anticathode, a concave cathode for focusing cathode rays upon said' anti-cathode, and means for independently heating a portion of the concave surface of said cathode to a 4temperature to emit corpuscles.

39. In vacuum tube apparatus, the combination with a cathode having a concave face, a portion disposed near the center of said surface having. a small heat capacity, the contour of its face being approximately the same asthat of the cathode face, of heating means for heating said portion.

40. In vacuum tube apparatus, an electrode having a concave face, a portion of which only 1s corpuscle emitting, a part at least of said corpuscles being emitted independently of bombardment of the electrode.

41. In vacuum tube apparatus, an electrode element having a concave corpuscle emitting face, a part at least of said co1'- puscles being emitted independently of bombardment of the electrode element.

42. In vacuum tube apparatus, an electrode having a concave face, a portion of which only is corpuscle emitting, said portion emitting corpuscles independently of the presence or absence of gas in the tube.

43. In vacuum tube apparatus, an electrodeI element having a concave corpuscle emitting face, said element emitting corpusles independently of the presence or absence of gas in the tube.

In testimony whereof I have hereunto aiixed my signature in the presence of the two subscribing witnesses.

EDWIN WALKER KELLY. Witnesses:

ELnANoR T. MGCALL, N nLLm B. EVANS. 

